The present invention relates to a telephone circuit, more particularly to a telephone circuit for connecting two simultaneously available telephones using a pair of twisted-pair cables in a telephone exchange. The present invention relates to a telephone circuit which can set up two telephones in each guest room without any additional construction of a cable in a hotel in which only a pair of twisted-pair cables have been already appointed.
Recently, a case in which a portable personal computer is connected to a telephone in a guest room in a hotel and information is transferred has increased with prevalence of the portable personal computer. Furthermore, it has been desired that the telephone is available during transferring the information by the personal computer. When a plurality of conventional analog telephones are set up in the guest room of the hotel, a style in which two or three telephones are in parallel connected to an end terminal of the pair of twisted-pair cables connected to a telephone exchange, that is, a branch connection, has been generally adopted.
Such branch connection has inexpedience that when one telephone is in use, other telephones are not available. Moreover, vast amount of construction costs are needed when it is tried to additionally set-up telephones by incorporating more cables in each guest room.
As a prior art in which a transmission line of plural channels such as 2B+D is formed on a pair of twisted-pair cables and two digital telephones are connected thereto, there is Japanese Patent Laid-Open No. 5(1993)-350696. In the technique disclosed in the gazette, though the two telephones are simultaneously available, there is the following problem to be solved.
Specifically, in this prior art, a bipolar code of Alternate Mark Inversion (hereinafter referred to as AMI) is used for a line code, and pulses transmitted from the two telephones are multiplexed on the twisted-pair cables according to an AMI code rule. Accordingly, polarities of the pulses which one telephone transmits are monitored by the other telephones and codes of the pulses which one telephone transmits must be determined. Furthermore, as a case for connecting a telephone to an end terminal of the twisted-pair cable, there are the following two cases. One is that one telephone is connected to the end terminal of the twisted-pair cables. The other is that two telephones are connected thereto. Since impedance of the end terminal of the twisted-pair cables changes depending on the number of telephones connected to the end terminal of the twisted-pair cables, the following countermeasures are necessary. Specifically, transmission waveforms must be automatically adjusted while observing receipt waveforms or a detection level of the receipt waveforms must be automatically adjusted. Therefore, a pulse transmitter-receiver circuit is complicated.
Furthermore, when a conventional analog telephone is called up, a ringing signal of a high alternate voltage (e.g., 75 Vrms, 16 Hz) is used. A high alternate voltage generator for producing the ringing signal is necessary for an exchange connecting the telephone and equipment, which are set up on a base side. The reason why the high alternate voltage is used is that an electromagnetic bell was used in the conventional telephone. Accordingly, the conventional telephone adopts such style. However, telephones which have been recently manufactured are almost computerized. In such telephones, while a ringing signal is detected, a ring back tone for calling up a called-up person is generated by a tone ringer generating circuit using a low voltage. To be more specific, because it is necessary only that a signal indicating a call request is transmitted to a telephone from an exchange and equipment on a base side, the high alternate voltage generator is expensive and unnecessary.
In view of the drawbacks of the conventional telephone, the object of the present invention is to provide a telephone circuit economically which makes it possible to set up simultaneously available two telephones on a remote end terminal or an end portion of a cable by utilizing an existing pair of twisted-paired cables.
Another object of the present invention is to provide a telephone circuit which makes it possible to set up two simultaneously available telephones on a remote end terminal or an end portion by utilizing an existing pair of twisted-pair. cables connected to a telephone exchange, without any additional construction of a cable, and particularly which makes it possible to set up a plurality of telephones in a guest room of a hotel economically.
Still another object of the present invention is to economically realize a telephone circuit which transmits a ringing signal between first and second telephones by a polarity-reversal signal and makes it unnecessary to provide a high alternate voltage generating circuit that has been necessary, thus making it possible to set up a plurality of simultaneously available telephones on a remote end terminal of a cable or an end portion thereof.
A telephone circuit of the present invention comprises,
a first circuit connected to a telephone exchange by a pair of lines, the first circuit establishing first and second information channels and a signal channel bidirectionally between a telephone exchange and a first telephone, thus sending and receiving user information and a control signal; and
a second circuit connected to a second telephone by a pair of lines, which transmits/receives an analog signal of a voice band and a DC or AC control signal, and transmits/receives the second information channel and a control signal to/from the first circuit,
wherein the first circuit allocates to the first telephone the first information channel of the bidirectional channels between the telephone exchange and the first telephone, allocates the second information channel to the second telephone, and allocates a signal channel to the control signals of the first and second telephones.
To achieve the foregoing objects, the present invention has one feature in that a telephone exchange and a first telephone are connected by a pair of twisted-pair cables, or the telephone exchange and the first telephone are connected by a 2-wire digital line or an ISDN line (2B+D) by a point-to-point contact, a digital signal channel of the ISDN line (2B+D) is established bidirectionally between the telephone exchange and the first telephone, and performs reciprocation for user information and a control signal between the telephone exchange and the first telephone.
The present invention has another feature in that an interface circuit is provided for connecting a first telephone to a second analog telephone, and the first telephone and a second telephone are connected by a pair of twisted-pair cables (2-wire analog line), and an analog signal of a voice band and a DC/AC control signal are sent and received between the first and second telephones. In contrast, in a general ISDN basic interface, a plurality of ISDN terminals are connected to a 4-wire digital line (2B+D) via respective buses.
Furthermore, a detailed way to achieve the telephone circuit will be described as follows.
The B-channel of the foregoing 2B is allocated to the foregoing first telephone, and the other B-channel is allocated to the foregoing second telephone. The foregoing D-channel signal can be shared by control signals for the foregoing first and second telephones.
The bidirectional (2B+D) digital signal should be sent and received by a ping-pong transmission system. However, the transmission system is not limited to this, and an appropriate transmission system can be adopted.
It is possible to allow the foregoing first telephone to operate by supplying power from the foregoing telephone exchange thereto, the power being superposed on a signal on the pair of twisted-pair cables. It is possible to allow the foregoing second telephone to operate by supplying power from the foregoing first telephone thereto, the power being superposed on a signal on the pair of twisted-paired cables.
An on-hook/off-hook signal of the foregoing second telephone is transmitted by making and breaking a loop of the pair of twisted-paired cables, and the on-hook/off-hook signal can be transmitted to the foregoing telephone exchange after converting this signal to the foregoing D-channel control signal in the foregoing first telephone.
A dial signal (address signal) of the foregoing second telephone is transmitted by making and breaking a loop of the pair of twisted-paired cables, and the dial signal thereof is transmitted to the foregoing telephone exchange after converting this signal to the foregoing D-channel control signal in the foregoing first telephone. Alternatively, a DTMF signal is transmitted onto the pair of twisted-paired cables, and can be transmitted to the foregoing telephone exchange via the foregoing B-channel after converting this signal to a digital signal in the foregoing first telephone.
Transmission request information relating to a ringing signal for the foregoing second telephone is transmitted to the foregoing first telephone from the foregoing telephone exchange via the foregoing D-channel, and the transmission request information is converted to an AC bell-ringing signal in the foregoing first telephone based on the transmission request information. The AC bell-ringing signal is transmitted to the foregoing second telephone.
Transmission request information relating to a ringing signal for the foregoing second telephone is transmitted to the foregoing first telephone from the foregoing telephone exchange via the foregoing D-channel, and the transmission request information is transmitted to the foregoing second telephone by a polarity reversal signal of a voltage applied onto the pair of twisted-paired cables in the foregoing first telephone based on the transmission request information.
The foregoing second telephone generates ring back tone during a period of time when the polarity is inverted in response to the foregoing polarity-reversal signal from the foregoing first telephone.
A circuit for generating the ring back tone generated by the foregoing second telephone operates by current flow by the polarity-reversal signal from the foregoing first telephone, by utilizing a diode characteristic.
Transmission request information relating to a message waiting signal for the foregoing second telephone is transmitted to the foregoing first telephone from the foregoing telephone exchange via the foregoing D-channel, and a DC power source supplied from the foregoing telephone exchange via the pair of twisted-paired cables is converted in the foregoing first telephone based on the transmission request information to a message waiting signal which is to be transmitted to the foregoing second telephone. The message-waiting signal is transmitted to the foregoing second telephone.
Although the foregoing first telephone should mount circuits and parts necessary for connecting the foregoing first telephone thereto on its detachable baby board, the foregoing first telephone is not limited to such structure.
A signal sent and received on the foregoing D-channel is constituted by a packet. A packet for loading information relating to the foregoing first telephone to be sent and received and a packet for loading information relating to the foregoing second telephone to be sent and received are separately prepared, and a telephone identifier is provided in each packet, respectively, and both packets can be identified from each other.
The foregoing second circuit provides an alternation switch for switching a downstream signal of the second information channel to a speaker built in the foregoing first telephone, based on transmission instruction information from the telephone exchange to the speaker in the foregoing first telephone via the signal channel.
All or part of a power source for supplying power from a first telephone to a second telephone by superposing the power on a signal on a pair of lines, a power source for a message waiting signal, and a ringing power source are supplied with power from a power source or an external power source which are supplied with power from a telephone exchange to the first telephone by superposing the power on a signal on a pair of lines.